Shelf



FIG. 1 is a front elevational view of a shelf showing my new design;

FIG. 2 is a rear elevational view thereof; and

FIG. 3 is a left elevational view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top side view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view of a shelf showing my new design.

The broken lines in the figures are for the purposes of illustrating portions of the shelf, which form no part of the claimed design. 

CLAIM The ornamental design for a shelf, as shown and described. 